Polyphase electrical transformer construction having vertically superposed winding structures with cooling ducts



March 4. 1969 BRQVERMAN 3,431,524

POLYPHASE ELECTRICAL TRANSFORMER CONSTRUCTION HAVING VERTICALLYSUPERPOSED WINDING STRUCTURES WITH COOLING DUCTS Filed June a, 1966Sheet Z of 25:51 "HUM! MN 5 HI I I n I FIG.3.

INVENTOR Alvin Y Brovermun ATTORNEY March 4. 1969 .A. Y. BROVERMAN3,431,524

POLYPHASE ELECTRICAL TRANSFORMER CONSTRUCTION HAVING VERTICALLYEUPBRPOSED WINDING STRUCTURES WITH COOLING DUCTS Filed June a, 1966Sheet 2 of UCTION HAVING VBRTICALLY TH COOLIN March 4. 1969 G DUCTSSheet 3 or:

A. Y. BROVERM POLYPHASE] ELECTRICAL T NSF'ORMER CONSTR SUPERPOSBD WI NGSTRUCTURES WI Filed June :2, 1966 FIG6 FIG.8.

United States Patent 9 Claims ABSTRACT OF THE DISCLOSURE A fluid cooled,polyphase electrical transformer of the core-form type, having aplurality of vertically spaced, superposed winding assemblies disposedon a magnetic core. The winding assemblies have cooling ducts thereinwhich extend horizontally between the ends of each of the windingassemblies, with the cooling ducts being arranged to provide adiagonally upward flow of the cooling fluid between the ends of thewinding assemblies.

This invention relates in general to electrical inductive apparatus,such as transformers, and more particularly to electrical transformersof the polyphase core-form type.

Polyphase transformers of the core-form type, such as three-phasetransformers, conventionally utilize a magnetic core having threevertically disposed leg portions, which are horizontally spaced, andconnected by two horizontally disposed, vertically spaced yoke portions.An electrical phase winding structure is disposed on each leg portion ofthe magnetic core, which includes concentrically disposed high and lowvoltage windings or coils, with certain layers of conductor turns of thewindings or coils being separated by duct forming means to providevertically disposed cooling ducts within the winding structure. Thefluid insulating dielectric in the transformer, by virtue of theinherent vertical thermal head therein, flows upwardly through thecooling ducts, removing heat from the conductor turns which form thewindings.

The horizontally spaced winding arrangement of the conventionalpolyphase core-form transformer requires a substantial amount of floorspace, as well as a large enclosure or tank which requires a largequantity of dielectric insulating fluid. In an effort to reduce thefloor space, tank size and amount of dielectric insulating fluidrequired, the electrical phase windings have been disposed one above theother, by rotating the magnetic corewinding structure 90 and standingthe structure on one of the ends. This arrangement, however, has provento be unsatisfactory because the cooling ducts through the windingstructure with this arrangement are horizontally disposed, with thethermal head being substantially the same at each end of the ducts.Thus, there is very little flow of the fluid dielectric through thecooling ducts, resulting in a substantial rise in temperature of thewinding turns. Thus, the rating of the transformer has to besubstantially reduced, or the size of the cooling system has to besubstantially increased to insure that the electrical phase windings donot exceed a predetermined maximum temperature.

Electrical phase windings have also been disposed one above the other,utilizing the same position in which they are disposed in theconventional horizontally spaced windings, which solves the coolingproblem, as the cooling ducts are disposed in a vertical manner. Thislatter arrangement, however, while reducing the floor space, has thedisadvantage of substantially increasing the length of the magneticcircuit. This latter arrangement requires a magnetic core havingsubstantially the same configuration as a three-phase magnetic core ofthe shell-form type, with the substantial increase in the length of themagnetic circuit deleteriously affecting the weight and losses of thetransformer. Also, with this core arrangement the magnetic circuitextends both above and below the upper and lower phase windings, whichsubstantially increases the height of the transformer.

It would be desirable to be able to utilize the conventional core-formtype of magnetic core and vertically disposed phase windings, if thisstructure could be utilized without de-rating the transformer, andwithout having to substantially increase the size of the cooling system.

Accordingly, it is an object of this invention to provide a new andimproved polyphase electrical transformer of the core-form type.

Another object of the invention is to provide a new and improvedpolyphase transformer of the core-form type in which the electricalwindings of each phase are superposed, each on a separate leg of amagnetic core.

A further object of the invention is to provide a new and improvedthree-phase transformer of the core-form type which has three windingsections, each disposed on a separate horizontally disposed leg of themagnetic core, with the winding sections being located vertically withrespect to one another, and which will operate at substantially the samerating and temperature rise as similarly constructed windings disposedon vertically disposed, horizontally spaced magnetic core legs.

Briefly, the present invention accomplishes the above cited objects byproviding a polyphase transformer of the core-form type which includes amagnetic core-winding structure disposed in an enclosure or tankcontaining a fluid dielectric. The magnetic core has a plurality ofhorizontally disposed, vertically spaced core legs, with the electricalwindings being disposed on the core legs. Duct forming means areutilized in the electrical windings of each phase of the transformer,which allows a multi-directional flow of the dielectric fluid throughthe windings. In addition to a horizontal flow of the cooling fluid, theduct formers allow an upward, or diagonally upward flow of the fluidwhich takes advantage of the vertical thermal head which inherentlyexists in the cool ing fluid between the upper and lower location ofeach phase winding in the dielectric fluid. Thus, each phase winding iscooled by a continuous fiow of the dielectrip fluid through the coolingducts in the winding phase.

Further objects and advantages of the invent-ion will become apparentfrom the following detailed description, taken in connection with theaccompanying drawings, in which:

FIGURE 1 is a front elevational view, partially cut away, of atransformer constructed according to the teachings of the invention;

FIG. 2 is a side elevational view, partially cut away, of thetransformer shown in FIG. 1;

FIG. 3 is a plan view, partially cut away, of the transformer shown inFIG. 1,

FIG. 4 is an enlarged fragmentary view, partially cut away, of thetransformer view shown in FIG. 2;

FIG. 5 is a perspective view of a duct former construction which may beused in the transformer shown in FIGS. 1-4;

FIG. 6 is a plan view of another d-uct former construction which may beused in the transformer shown in FIGS. 1-4;

FIG. 7 is an end view of the duct former construction shown in FIG. 6;and

FIG. 8 is a plan view of still another duct former construction whichmay be used in the transformer shown in FIGS. 1-4.

Referring now to the drawings, and FIGS. 1, 2 and 3 in particular, thereis shown front, side and plan views, respectively, partially cut away,of a three-phase transformer 10 of the core-form type, which isconstructed according to the teachings of the invention. Transformer 10includes a magnetic core-winding assembly 12 disposed within a suitablecasing or tank 14, which is filled with a fluid dielectric, such as oil,to a predetermined level 16, which completely immerses the magneticcore-winding assembly 12.

The magnetic core-winding assembly 12 includes a magnetic core 18 andelectrical phase winding structures 20, 22 and 24. Magnetic core 18,which is preferably of the stacked type, but which may be of the Woundtype, if desired, includes winding leg portions 26, 28 and 30 forreceiving phase winding structures 20, 22 and 24, respectively, whichare horizontally disposed and vertically spaced in parallel relation ona common perpendicular plane. The ends of the leg portions 26, 28 and 30are connected by vertically disposed, horizontally spaced yoke portions32 and 34, which completes the three-phase magnetic core structure 18,forming two openings or windows 36 and 38 therein. Magnetic core 18 maybe constructed of a plurality of stacks of metallic laminations formedof grain oriented magnetic strip material, such as silicon steel, witheach stack of laminations forming a leg or yoke portion, which arearranged to form closed magnetic circuits about windows 36 and 38.Magnetic core 18 is held in assembled relation by suitable end frames 40and 42, which are disposed against the outer yoke laminations on eachside of yoke portions 32 and 34, respectively, and bolted or otherwisefastened to maintain the laminations of the magnetic core in tightcontacting relation. The end frames 40 and 42 may extend past the endsof the magnetic core structure 18, forming means for supporting themagnetic core-winding assembly 12 within the tank 14, and providingsupport points for various bridging members, such as tie rods 44 and 46,which aid in mechanically bracing and supporting the various phasewindings. Solid insulating members, such as insulating members 48 and 50may be disposed between the phase windings and the grounded portions ofthe structure, and also between the phase windings themselves.

The phase winding structures 20, 22 and 24 each include concentricallydisposed high and low voltage windings, wound about an opening forreceiving a leg portion of the magnetic core 18. Each phase windingstructure 20, 22 and 24 has low voltage terminals, such as terminals 52and 54 on phase winding 20, terminals 56 and 58 on phase winding 22, andterminals 60' and 62 on phase winding 24, which are interconnected toform a Y connection, as shown, a delta connection, or a T connection,and then connected to the low voltage output terminals 64, 66, 68 and70.

Each electrical phase winding structure also has high voltage terminals(not shown) which are interconnected to form a delta, Y, or Tconnection, and then connected to high voltage terminal bushings 72, 74and 76 via electrical conductors 73, 80 and 82.

Each phase winding structure may also have a plurality of tap positions(not shown) which are brought out of the windings to a terminal board 84via suitable electrical conductors, such as conductors '86, 88 and 90from electrical phase winding structure 20. The tap changer (not shown)is mounted in the space above the magneticcore winding assembly 12.

Each electrical phase winding structure 20, 22 and 24 has a plurality ofopenings which are located or disposed between certain layers ofconductor turns which form the electrical coils of the phase windingstructures, to allow the fluid dielectric to flow therethrough andremove heat from the electrical windings. The openings 100 are formed bysuitable spacers or duct forming means, which will bedescribed in detailhereinafter. It should be noted that the openings 100 have a lengthwhich extends between opposite ends of the phase winding structures, andthey have a narrow, elongated cross-section, With the elongateddimension being oriented in a substantially vertical manner.

Summarizing to this point, there has been disclosed a new and improvedpolyphase transformer of the coreform type, which requires very littlefloor space, because the phase winding structures 20, 22 and 24 aredisposed vertically one above the other, instead of the conventionalhorizontal spacing. Thus, the tank size is substantially reduced, aswell as the amount of fluid dielectric required. This structure thusprovides a substantial reduction in the size, weight and cost of thetransformer. Also, unlike other arrangements in which the phase windingsare vertically disposed, the magnetic core has the same magnetic circuitlength as magnetic core-winding arrangements of the core-form type inwhich horizontal spacing of the electrical phase winding structures isutilized. Further, the magnetic core does not extend above and below thewindings, as required in certain other vertically spaced windingarrangements, thus achieving the savings in floor space, weight andfluid dielectric without an excessive increase in the overall height ofthe transformer assembly. Certain prior art vertically spaced electricalphase windings, in order to dispose the cooling ducts or openings 100 ina vertical position, and thus maintain the phase windings in the sameorientation used in horizontally spaced electrical phase windings toprovide adequate cooling of the windings by thermal siphon of the fluiddielectric, are disposed on three separate vertically disposed legportions, all on a common center line. The return flux paths requiredwith this arrangement provide a magnetic core structure similar inconfiguration to a three-phase shell-form magnetic core structure,having six openings or windows in the magnetic core for receiving thethree electrical phase winding structures of a three-phase transformer.Thus, the length of the magnetic circuit is substantially increased,compared with the length of a three-phase magnetic circuit of a magneticcore of the core-form type. Also, the magnetic circuit necessarilyextends above and below the upper and lower phase windings, whichsubstantially increases the height of the overall transformer structure.

This invention makes it possible to dispose the electrical phasewindings on individual horizontal disposed, vertically spaced legportions of a magnetic core, by providing duct former means in the ductopenings 100 in the electrical phase winding structures 20, 22 and 24,which allows a multi-directional flow of dielectric fluid under theinfluence of the thermal head inherent in the dielectric fluid when theelectrical transformer is energized.

More specifically, referring to FIGS. 4 and 5, there is shown in FIG. 4an enlarged, fragmentary view, partially cut away, of the electricalphase winding structure 20 of the transformer 10 shown in FIGS. 1, 2 and3, and FIG. 5 illustrates a duct former construction used in the phasewinding .20 shown in FIG. 4.

Electrical phase winding structure 20 includes a winding tube 102,formed of a suitable electrical insulating material, such as multiplelayers of pressboard, which provides a form for the various coils orwinding sections of electrical phase winding structure 20, as well asproviding an opening for receiving leg portion 26 of magnetic core 18,and also provides electrical insulation between the electrical phasewinding structure 20' and the grounded magnetic core leg 26. Phasewinding structure 20 includes concentrically disposed low and highvoltage winding sections 104 and 106, respectively, separated byhigh-low solid insulating means 108. The low voltage section 104includes a plurality of layers 110 of electrically insulated electricalconductor turns, formed of copper or aluminum, or other suitableelectrical conductive material. The winding turns may be in the form ofa sheet or strip, or they may be in wire form, wound about insulatingtube 102. If the conductor turns are formed of sheet or strip, eachlayer may include only one conductor turn. If the conductor turns areformed of electrically conductive wire, each layer will include aplurality of conductor turns. Certain layers of conductor turns areseparated, at opposite ends of the low voltage winding section, by ductformer means 120, which form cooling ducts or openings 100 at the endsof the phase winding which extend outwardly on each side of the magneticcore 18. Duct former means 120 may also be disposed between the high andlow voltage winding sections 106 and 104, as shown in FIG. 4.

In like manner, the high voltage winding section .106 includes aplurality of layers 122 of insulated sheet or wire electrical conductorturns wound about the low volt age section 104, and also having certainlayers of conductor turns separated, at opposite ends of the highvoltage section, by the duct former means 120. It will be noted that thewinding leg portions of the magnetic core 18, such as leg 26, aresubstantially rectangular in shape, and that the phase windings are alsosubstantially rectangular in shape, which provides two areas at oppositeends of the winding structure where the layers of conductor turns aresubstantially vertical. These areas of the winding structure extendoutwardly away from the magnetic core means, and it is these two areasin which the cooling ducts or openings 100 are disposed.

In this embodiment of the invention, the duct former means 120 is of thecorrugated type, having a series of parallel waves and furrows, andformed of pressboard, or other suitable solid electrical insulatingmaterial. The corrugated duct former means 120 is disposed with theparallel waves and furrows extending between the two opposite ends ofthe winding structure, which provide a plurality of openings 124 in eachof the cooling ducts 100. In the prior art, these openings 124 would beisolated from one another, and being disposed in a direction which issubstantially perpendicular to the direction of the winding layers 110and 122 of the low and high voltage winding sections 104 and 106, therewould be little difference in the thermal head which would exist atopposite ends of the horizontal openings 124. Thus, there would be verylittle, if any, flow of the dielectric fluid through the cooling ducts,resulting in an excessive temperature rise within the windingstructures, if the windings are operated without de-rating.

FIG. 5 illustrates a perspective view of the duct former means 120,constructed according to the teachings of one embodiment of theinvention. Specifically, duct former means 120 is corrugated, having aseries of connected furrows 126 and waves 128, which provide theplurality of openings 12.4 when disposed between the layers of conductorturns which form the high and low voltage winding sections. Thus, thecorrugated edge 130 of the duct former means 120 may be the edge whichmay be seen in the View of the phase winding structure 20 in FIG. 4. Inother words, the corrugated edges of the duct former means 120, such asedge 130, appear at both end surfaces of the phase winding structure,while the straight edges of the duct former means 120, such as edge 132,are located within the openings 100', running between the opposite endsof the phase winding structure. Thus, the layers of conductor turns, and122 of the low and high voltage winding sections 104 and 106, across theduct former means in a direction which is substantially perpendicular toits straight edges, as shown by arrow 134.

In order to promote an upward, or diagonally upward, flow of dielectricfluid through the openings 100, as well as allow the dielectric fluid toenter the ends of the openings 100, the corrugated duct former means 120has a plurality of slots or openings 136 and 138 disposed therein, withopenings 136 being disposed in the wave portions and openings 138 beingdisposed in the furrow portions. The openings have a predetermined widthand length, and are spaced a predetermined distance apart. The depth ofthe slot or openings in each of the waves and furrows may besubstantially to the center line 140 of the overall thickness T of thecorrugated duct former means 120, or any other suitable depth, as longas the mechanical strength of the duct former means 120 is not seriouslyimpaired.

In order to promote a diagonally upward flow of fluid dielectric fromone end of the phase winding structure 20 to the other, the lengthdimension of the openings 136 and .138 should be disposed at an anglewith respect to the corrugated edges, or with respect to the straightedges of the duct former means, with the angle, such as the angle Ashown in FIG. 5, preferably being 45. However, the actual angle withrespect to the direction of the waves and furrows or with respect to theedges of the duct former means may vary quite widely on either side of45, depending upon the particular dimensions of the electrical phasewinding structure.

The angled openings 136 and 138 in the duct former means may be veryeasily formed, for example, by saw cuts.

Thus, duct former means 120, with the plurality of openings 136 and 138therein, allow an upward flow of cooling fluid in the duct openings 100,with the angled direction of the Openings promoting a diagonally upwardcross flow of the fluid dielectric, which thus takes ad vantage of theinherent upward flow of dielectric fluid within the transformer tank dueto the heating of fluid by the magnetic core-winding assembly 12 shownin FIG. 1. The heated fluid, after circulating through the cooling ducts100 may be circulated through external heat exchanger means (not shown),if desired, and returned to the bottom of the tank 14 for recirculation.While the dielectric fluid will circulate through the cooling ducts 100by the natural thermal siphon etfect of the dielectric fluid, pumpingmeans (not shown) may also be utilized to increase the flow of thecooling fluid through the transfonmer tank, through the cooling ducts100 in the electrical phase winding structures, and through anyauxiliary heat exchanger means which may be utilized.

A 500 kva. three-phase transformer was constructed according to theteachings of the invention, using the duct former means 120 shown inFIG. 5. The transformer was load tested, both in the position shown inFIG. 1, with the electrical phase winding structures vertically spaced,and in the conventional position wherein the electrical phase windingstructures are horizontally spaced. The temperature rise of theelectrical conductors were Within one degree of one another in the twopositions, illustrating the effectiveness of the duct former means shownin FIG. 5 in promoting flow of the fluid dielectric through the ducts.Using duct formers similar to that shown in FIG. 5, but without theopenings 136 and 138 disposed in the waves and furrows, causes asubstantial increase in the conductor temperature in a transformerhaving vertically spaced phase windings as shown in FIG. 1, comparedwith transformers having horizontally spaced windings, which makes thevertical type structure in this instance completely unsuitable.Therefore, the objections to vertically spaced phase windings have beenovercome by the teachings of this invention, making it possible toachieve substantial savings in floor space, savings in the amount offluid dielectric required, and savings in the overall weight of thetransformer structure. For example, on a 500 kva. three-phasetransformer, the savings in weight of a transformer constructedaccording to the teachings of this invention, over the conventionalhorizontal position of the electrical phase windings, exceeds 20%.

The duct former means 120 shown in FIG. illustrates one arrangement forachieving an upward as well as a cross flow of cooling fluid through thephase winding structures of an electrical polyphase transformer. FIGS.6, 7 and 8 illustrate other duct former means which may be utilized toachieve this result.

Specifically, FIGS. 6 and 7 illustrate plan and edge views,respectively, of a suitable duct former means 150. Duct former means 150is constructed of a sheet 152 formed of electrical insulating material,such as pressboard having two major opposed surfaces. A plurality ofducts or paths through the cooling duct, when it is disposed betweencertain layers of winding turns, are provided by the plurality ofdiscrete insulating blocks 154 which are attached to one or both of themajor opposed surfaces of the sheet member 152 in a predetermined spacedpattern. For example, if edge 156 of the duct former means 150 isassumed to be the bottom edge of the duct former means as disposed inthe phase winding structure shown in FIG. 4, and with the arrows 158indicating the direction of the phase winding turns, the blocks 154 maybe disposed in spaced relation, and oriented such that the direction ofthe winding turns proceeds diagonally across the blocks, from one cornerto the opposite corner, assuming the blocks to be square. This providesdiagonally upward paths for the cooling fluid, such as shown by arrows160 and 162.

While the discrete block members 154 are illustrated in FIG. 6 as beingsquare, they may also be rectangular in nature in which two oppositesides have different lengths than the two remaining opposite sides.

FIG. 8 shows a plan view of still another duct former means 170 whichmay be utilized with the invention. Like the embodiment of FIGS. 6 and7, this embodiment also includes a sheet member 172 of insulatingmaterial, having two major opposed sides, but instead of having discretespaced block members, this embodiment utilizes spaced strip members 174,which are suitably attached to one or both of the major opposed surfacesof the sheet member. Assuming edge 176 of sheet 172 to be the bottomedge of the duct former means, as disposed in a phase winding structuresuch as that shown in FIG. 4, and with arrow 178 indicating thedirection of the conductor turns of the phase winding, the strip membersare disposed in spaced relation, and inclined upwardly at apredetermined angle, such as 45 Thus, the cooling dielectric fluid mayenter the openings between the strip members 174 at one edge or end ofthe electrical phase winding structure and flow diagonally upward toexit at the opposite end of the phase winding structure.

In summary, there has been disclosed a new and improved polyphasetransformer construction of the coreformer type, which requiressubstantially less floor space, requires less dielectric fluid, requiresa smaller casing or tank, and which weighs less than similarly ratedpolyphase core-form transformers of the prior art. Further, thedisclosed transformer construction is less costly to manufacture, due tothe smaller enclosure and reduction in the amount of dielectric fluidrequired.

Since numerous changes may be made in the above described apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all matter contained in theforegoing description or shown in the accompanying drawings, shall beinterpreted as illustrative, and not in a limiting sense.

I claim as my invention:

1. Electrical inductive apparatus comprising a tank,

dielectric fluid disposed in said tank,

magnetic core means having a plurality of horizontally disposed,vertically spaced winding leg portions,

a plurality of electrical phase winding assemblies each having first andsecond ends and an opening for receiving a magnetic core extendingbetween its ends, said electrical phase winding assemblies each having aplurality of layers of conductor turns disposed coaxially about the coreopening,

one of said electrical phase winding assemblies being disposed abouteach of the winding leg portions of said magnetic core means, forming amagnetic corewinding assembly, said magnetic core-winding assembly beingdisposed in said tank and immersed in said dielectric fluid,

duct former means disposed between predetermined layers of conductorturns in each of the electrical phase winding assemblies, forming atleast one cooling duct which extends between openings at the first andsecond ends of said electrical phase winding assemblies, said at leastone cooling duct having a narrow, elongated cross section, and orientedwith the elongated dimension being substantially vertical, said ductformer means being constructed to provide a plurality of dielectricfluid flow paths through said at least one cooling duct which extenddiagonally upward between the ends of said electrical phase windingassemblies,

said dielectric fluid flowing through said cooling ducts by thermalsiphon effect when the electrical inductive apparatus is energized.

2. The electrical inductive apparatus of claim 1 wherein said electricalinductive apparatus is a three-phase transformer of the core-form type,and said magnetic core means includes three horizontally disposed,vertically spaced winding leg portions and two vertically disposed,horizontally spaced yoke portions which connect said winding legportions.

3. The electrical inductive apparatus of claim 1 wherein the winding legportions of said magnetic core means and said electrical phase windingassemblies have a substantially rectangular cross section.

4. The electrical inductive apparatus of claim 1 wherein the winding legportions of said magnetic core means and said electrical phase windingassemblies have a substantially rectangular cross section, forming firstand second areas in said electrical phase winding assemblies in whichthe layers of conductor turns in said electrical phase windingassemblies are substantially vertically oriented, said duct former meansbeing disposed in said first and second areas of each of said electricalphase winding assembles, forming a plurality of cooling ducts therein.

5. The electrical inductive apparatus of claim 1 wherein said ductformer means is formed of a corrugated electrical insulating memberhaving a series of parallel wave and furrows, said parallel waves andfurrows each having a plurality of openings disposed therein havingpredetermined width and length dimensions, at least one of saidcorrugated electrical insulating members being disposed in each of saidelectrical phase winding assemblies, and oriented with the waves andfurrows extending between the first and second ends of said electricalphase winding assemblies.

6. The electrical inductive apparatus of claim 5 in which the lengthdimension of the openings in said parallel waves and furrows is disposedat an acute angle relative to the direction of the parallel waves andfurrows which promotes the diagonally upward flow of the dielectric-fluid between the ends of the phase winding assemblies.

7. The electrical inductive apparatus of claim 1 wherein said ductformer means is formed of an electrical insulat- 9 ing member having twomajor opposed sides, said electrical insulating member having aplurality of spacer members having a predetermined shape attached to atleast one of its major sides in a predetermined pattern which providesthe diagonally upward dielectric fluid flow paths in said at least onecooling duct.

8. The electrical inductive apparatus of claim 7 wherein the pluralityof spacer members are discrete blocks having a substantially rectangularcross section, said discrete blocks being disposed in spaced relationand oriented to provide the diagonally upward dielectric fluid flowpaths in said at least one cooling duct.

9. The electrical inductive apparatus of claim 7 wherein the pluralityof spacer members are strips of electrical insulating material disposedin spaced parallel relation at a predetermined angle relative to theedges of the major sides of said electrical insulating member,

providing the diagonally upward dielectric fluid flow paths in said atleast one cooling duct.

References Cited UNITED STATES PATENTS 2,424,973 8/1947 Edmonds 336-60XR 3,071,845 1/1963 Leonard et al. 336--60 XR 3,151,304 9/1964 Miller336-60 XR 3,195,084 7/1965 Book 336-207 XR 3,201,728 8/ 1965 McWhirter336-60 3,237,136 2/1966 Ford 336-207 XR 3,252,117 5/1966 Fischer 336185XR 3,302,149 1/1967 Forsha 33660 LEWIS H. MYERS, Primary Examiner.

THOMAS J. KOZMA, Assistant Examiner.

